﻿using System;
using System.Collections.Generic;
using System.Text;
using System.ComponentModel;

namespace Qreed
{
    /// <summary>
    /// Static class with an improved <see cref="System.Convert.ChangeType"/> function, which 
    /// supports nullable value types. I grabbed the function from an old blog of Peter Johnson (modified it a little bit).
    /// </summary>
    public static class Convert
    {
        /// <summary>
        /// Returns an Object with the specified Type and whose value is equivalent to the specified object.
        /// </summary>
        /// <param name="value">An Object that implements the IConvertible interface.</param>
        /// <param name="conversionType">The Type to which value is to be converted.</param>
        /// <returns>An object whose Type is conversionType (or conversionType's underlying type if conversionType
        /// is Nullable&lt;&gt;) and whose value is equivalent to value. -or- a null reference, if value is a null
        /// reference and conversionType is not a value type.</returns>
        /// <remarks>
        /// This method exists as a workaround to System.Convert.ChangeType(Object, Type) which does not handle
        /// nullables as of version 2.0 (2.0.50727.42) of the .NET Framework. The idea is that this method will
        /// be deleted once Convert.ChangeType is updated in a future version of the .NET Framework to handle
        /// nullable types, so we want this to behave as closely to Convert.ChangeType as possible.
        /// This method was written by Peter Johnson at:
        /// http://aspalliance.com/author.aspx?uId=1026.
        /// </remarks>
        public static object ChangeType(object value, Type conversionType)
        {
            // Note: This if block was taken from Convert.ChangeType as is, and is needed here since we're
            // checking properties on conversionType below.
            if (conversionType == null)
            {
                throw new ArgumentNullException("conversionType");
            } // end if

            // If it's not a nullable type, just pass through the parameters to Convert.ChangeType

            if (conversionType.IsGenericType &&
              conversionType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
            {
                // It's a nullable type, so instead of calling Convert.ChangeType directly which would throw a
                // InvalidCastException (per http://weblogs.asp.net/pjohnson/archive/2006/02/07/437631.aspx),
                // determine what the underlying type is
                // If it's null, it won't convert to the underlying type, but that's fine since nulls don't really
                // have a type--so just return null
                // Note: We only do this check if we're converting to a nullable type, since doing it outside
                // would diverge from Convert.ChangeType's behavior, which throws an InvalidCastException if
                // value is null and conversionType is a value type.
                if (value == null)
                {
                    return null;
                } // end if

                // Qreed: little modification here if we're getting a empty string

                if (value.GetType() == typeof(string))
                {
                    string s = (string)value;
                    s = s.Trim();
                    if (s == string.Empty)
                        return null;
                }

                // It's a nullable type, and not null, so that means it can be converted to its underlying type,
                // so overwrite the passed-in conversion type with this underlying type
                NullableConverter nullableConverter = new NullableConverter(conversionType);
                conversionType = nullableConverter.UnderlyingType;
            } // end if

            // Now that we've guaranteed conversionType is something Convert.ChangeType can handle (i.e. not a
            // nullable type), pass the call on to Convert.ChangeType
            return System.Convert.ChangeType(value, conversionType);
        }
    }
}
